Crossover Study of Proportional Assist Versus Assist Control Ventilation in Infants with Evolving or Established BPD

Division of Asthma, Allergy and Lung Biology, MRC Centre for Allergic Mechanisms in Asthma, Kingís College
London

Background: During assist control ventilation (ACV), ventilator inflations are triggered by the onset of the infantís respiratory
efforts. In contrast, during proportional assist ventilation (PAV) ventilator pressure is servo controlled throughout
each respiratory cycle. In addition, the ventilator can provide inflation pressure in phase with the tidal volume
change in order to reduce the compliance load (elastic unloading) and in phase with the flow volume change to
reduce the resistance load (resistive unloading). We have previously demonstrated in a one hour cross over
period study PAV compared to ACV was associated with a significantly lower work of breathing and oxygenation
index and higher respiratory muscle strength (1). We, therefore, hypothesized that PAV compared to ACV would
result in a higher oxygenation index over a four hour period, the longest time PAV has been studied in vivo.

Methods: A randomised crossover study in prematurely born infants, ventilator dependent beyond the first week after birth
was undertaken. Prior to the start of each study, the infantís compliance was determined using the results from
the Stephanie ventilator, which delivered both ACV and PAV. During PAV, 100% elastic unloading was used. At
the end of each four hour period on ACV and PAV, the oxygenation index was calculated. The planned sample
size was 18 infants to allow a detection between the two ventilator modes of a difference equivalent to 0.7 SD in
the oxygenation index with 80% power and a two sided significance of 5%.

Results: Infants with a median gestational age 25 (range 24-33) weeks were studied at a median postnatal age of 19
(range 10-105) days. Their median baseline compliance was 0.4 (range 0.3-1.1) mls/cmH2O and resistance was
155 (range 66-252) cmH2O/l/sec. Recruitment was stopped at eight patients, as all their OI results were in
favour of PAV (p=0.004). The median FiO2 (p=0.049), the median mean airway pressure (p=0.012) and the
median oxygenation index (p=0.012) were all lower on PAV.

Conclusion: These results suggest that PAV compared to ACV is advantageous for prematurely born infants with evolving or
established BPD.